Ghost Arroyos

Ghost Arroyos

Ghost Arroyos by 

“It is hard to turn away from moving water.” Lyn Hejinian

Ghost Arroyos reveals forgotten, invisible waterways of San Francisco. For the Market Street Prototyping Festival, we sonically and visually highlighted an underground creek that emerged into a salt marsh just south of Market Street. During heavy rains, Hayes Creek would seep to the surface of the dunes, creating an ephemeral waterway.


Step 1:  Materials



– 8 siren/speaker metal enclosures (rust-resistant paint with front vents)

– 8 rechargeable wireless speakers (we used Polk Audio Omni S2)

– 8 MP3 players

– 8 locks for speaker boxes

– 25 cans of chalk spray

– 5 rolls of heavy duty duct tape

– 15 hose clamps (long enough to fit around light poles)

– engraving plastic for signage

– chipboard for stencils


– ladder (for installation)

– drill (with metal-cutting bit)

– laser cutting machine

– screwdriver


Step 2: Design



Waterway Mapping

We collected a number of historical maps and overlaid them onto existing aerials of San Francisco to determine the best place for marking the water. We also collaborated with a number of local historians and hydrologists to better understand the historical hydrology of the Bay Area.

Soundscape Design

Over the course of a few months, we collected sounds from around the Bay Area: from creek recordings to readings with local poets. These sounds were eventually engineered into a 10 minute-long recording that we looped during the festival.


Step 3: Fabrication


Speaker Box Fabrication

01 – Drill holes in metal enclosures for locks and hose clamp

02 – Paint metal enclosures

03 – Secure metal enclosures to nearby infrastructure (such as a light pole) using the hose clamp

04 – Test speaker quality and positioning

Chalk Application

01 – Using map overlays, determine where waterway will be marked

02 – Apply duct tape on ground to contain chalk spray

03 – Spray chalk evenly within duct tape boundary

Step 4: Installation


Due to the limited number of materials needed for the project, transportation to the festival was possible with a personal vehicle.

In an hour, we were able to assemble all 8 speaker boxes using the ladder, screwdriver and hose clamps.

The chalk spray application took two hours, but obviously this varies depending on the extent of the waterway being mapped.


Step 5: Interaction



Festival Takeaways:

01 – The installation location on the pedestrian island worked out well – so many different people interacted with the project while waiting to cross the street.

02 – While the noise levels of Market Street were high, people tended to lean into the speakers to listen to the recording, creating an intimate listening experience

03 – Over the course of a few days, the chalk tended to fade in highly trafficked areas. Next time, we will re-apply!

04 – Coordinating early and clearly about permitting in public spaces is extremely important! We were unable to execute the chalk portion of the installation as we had envisioned due to miscommunication.

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